A rolling bearing comprises an outer ring, an inner ring, a plurality of rollers arranged between the outer ring and the inner ring, and a retainer for holding the plurality of rollers in general. The retainer for holding the rollers includes various kinds such as a resin retainer, a pressed retainer, a ground retainer, and a welded retainer depending on its material and manufacturing method, and those are used based on purposes and characteristics. In addition, the retainer is an integrated type, that is, it comprises one annular part in general.
Here, since a rolling bearing that supports a main shaft of a wind-power generator on which a blade for receiving wind is mounted needs to receive a high load, the rolling bearing itself is large in size. Thus, since each constituent member such as a roller and a retainer is also large in size, it is difficult to produce and assemble such member. In this case, when each member can be split, it can be easily produced and assembled.
A split type retainer that is split along a split line extending in an axial direction is disclosed in European Patent Publication No. 1408248A2. FIG. 10 is a perspective view showing a retainer segment of the split type retainer disclosed in the European Patent Publication No. 1408248A2. Referring to FIG. 10, a retainer segment 101a has a plurality of pillar parts 103 extending in an axial direction so as to form a plurality of pockets 104 for holding rollers, and connection parts 102a and 102b extending in a circumferential direction so as to connect the plurality of pillar parts 103. On the inner diameter side of the pillar part 103 positioned on circumferential both sides of each pocket 104, an inner diameter-side roller stopper part is provided to prevent the roller housed in the pocket 104 from coming out toward the inner diameter side. Meanwhile, an outer-diameter side roller stopper part to prevent the roller from coming out toward the outer diameter side is not provided on the outer diameter side, and a flat part is provided. In addition, a projection 106a to keep a distance from an outer ring is provided at an end face of the pillar part 103 on the outer diameter side and a projection 106b (not shown) to keep a distance from an inner ring is provided at an end face of the pillar part 103 on the inner diameter side.
FIG. 11 is a sectional view showing a part of a rolling bearing containing the retainer segment 101a shown in FIG. 10. The constitution of a rolling bearing 111 containing the retainer segment 101a will be described with reference to FIGS. 10 and 11. The rolling bearing 111 has an outer ring 112, an inner ring 113, a plurality of rollers 114, and the plurality of retainer segments 101a, 101b and 101c holding the plurality of rollers 114. The plurality of rollers 114 are held by the plurality of retainer segments 101a and the like in the vicinity of a PCD (Pitch Circle Diameter) 105 in which the roller movement is most stable. The retainer segment 101a for retaining the plurality of rollers 114 is arranged such that circumferential end faces 107 abut on the circumferentially adjacent retainer segments 101b and 101c having the same configuration. The plurality of retainer segments 101a, 101b and 101c are continuously lined with each other, whereby one annular retainer contained in the rolling bearing 111 is formed.
According to the European Patent Publication No. 1408248A2, the retainer segment 101a keeps the distances from the outer ring 112 and the inner ring 113 by the projections 106a provided on the outer diameter side end face of the pillar part 103 and the projection 106b provided on the inner diameter side end face thereof. That is, the retainer segment 101a is guided by a track ring such as the outer ring 112 or the inner ring 113.
Since the retainer segments 101a, 101b and 101c are independent members and not coupled in the circumferential direction, when the retainer segment 101a is guided by the track ring, it is likely to move between the outer ring 112 and the inner ring 113, and its position is unstable in the radial direction.
More specifically, for example, in the case where the above rolling bearing 111 is set horizontally and used, when the retainer segment 101a is disposed at an uppermost position, the retainer segment 101a moves downward and an outer diameter surface 115 of the inner ring 113 positioned under it and the projection 106b provided on the inner diameter side end face of the pillar part 103 are brought into contact with each other, so that the retainer segment 101a is guided by the inner ring 113. Meanwhile, when the retainer segment 101a is disposed at an lowermost position, the retainer segment 101a moves downward and an inner diameter surface 116 of the outer ring 112 positioned under it and the projection 106a provided on the outer diameter side end face of the pillar part 103 are brought into contact with each other, so that the retainer segment 101a is guided by the outer ring 112. 
Thus, since the retainer segment 101a is likely to move in the radial direction while it is guided by the inner ring or the outer ring depending on its position in the rolling bearing 111, the radial position of the retainer segment 101a becomes unstable and noise could be generated and the retainer segment 101a could be damaged when the retainer segment 101a comes in contact with the outer ring 112 or the inner ring 113.
Furthermore, the projections 106a and 106b could scrape off an oil film on the track surfaces 115 and 116 at the time of the rotation of the bearing, which could lower the lubrication performance of the rolling bearing 111 considerably.